1. Field of the Invention
The present invention relates to an apparatus and method for transmitting/receiving downlink data channel signal transmission information in a cellular radio communication system. More particularly, the present invention relates to an apparatus and method for transmitting/receiving downlink data channel signal transmission information in a Cooperative Multi-Point (CoMP) cellular radio communication system in which a plurality of Base Stations (BSs) provide a Mobile Station (MS) with a service using a CoMP scheme.
2. Description of the Related Art
A cellular radio communication system has evolved to provide various high-speed large-capacity services to Mobile Stations (MSs). Examples of the cellular radio communication system include a High Speed Downlink Packet Access (HSDPA) mobile communication system, a High Speed Uplink Packet Access (HSUPA) mobile communication system, a Long-Term Evolution (LTE) mobile communication system, a LTE-Advanced (LTE-A) mobile communication system, a High Rate Packet Data (HRPD) mobile communication system proposed in a 3rd Generation Project Partnership 2 (3GPP2), and an Institute of Electrical and Electronics Engineers (IEEE) 802.16m mobile communication system.
The LTE mobile communication system has been developed to effectively support a high-speed radio packet data transmission, and may maximize a throughput of a cellular radio communication system using various Radio Access (RA) schemes. The LTE-A mobile communication system enhances the LTE mobile communication system, and has an enhanced transmission capability compared with the LTE mobile communication system.
A 3rd Generation (3G) radio packet data communication system of the related art such as the HSDPA mobile communication system, the HSUPA mobile communication system and the HRPD mobile communication system uses schemes such as an Adaptive Modulation and Coding (AMC) scheme and a channel adaptation scheduling scheme in order to enhance a transmission efficiency. Upon using the AMC scheme and the channel adaptation-scheduling scheme, a signal transmission apparatus may use an optimal modulation scheme and coding scheme at the most efficient time point by receiving partial channel status feedback information from a signal reception apparatus.
In a radio packet data communication system using the AMC scheme, a signal transmission apparatus may adjust an amount of data packets to be transmitted according to channel status. That is, if the channel status is bad, the signal transmission apparatus may keep a reception error probability in a target reception error probability which the signal transmission apparatus targets by decreasing the amount of data packets to be transmitted. On the other hand, if the channel status is good, the signal transmission apparatus may keep the reception error probability in the target reception error probability and effectively transmit many data packets by increasing the amount of data packets to be transmitted.
In a radio packet data communication system using the channel adaptation-scheduling scheme, the signal transmission apparatus selects an MS having good channel status among a plurality of MSs, and provides the selected MS with a service. So, a system throughput increases compared with a case where the signal transmission apparatus allocates a channel to an arbitrary MS, and provides the arbitrary MS with the service. Such system throughput increase is referred to as a ‘multi-user diversity gain’.
If the AMC scheme is used with a Multiple Input Multiple Output (MIMO) scheme, the AMC scheme may include a function for determining the number of spatial layers or a rank. In this case, the radio packet data communication system using the AMC scheme considers the number of layers to which a packet data is transmitted using the MIMO scheme as well as a code rate and a modulation scheme in order to determine an optimal data rate.
Generally, if an Orthogonal Frequency Division Multiple Access (OFDMA) scheme is used, a system throughput increase is expected compared with a case in which a Code Division Multiple Access (CDMA) scheme is used.
The reason why the system throughput is increased if the OFDMA scheme is used is that a radio packet data communication system may perform a frequency domain-scheduling scheme. The radio packet data communication system may acquire more throughput gains upon using a characteristic of which a channel status is varied according to a frequency like a case in which the radio packet data communication system acquires a throughput gain using the channel adaptation-scheduling scheme according to a characteristic of which a channel status is varied according to time. So, for a next generation cellular radio communication system, research is performed for changing the CDMA scheme used in a 2nd Generation (2G) cellular radio communication system and a 3G cellular radio communication system to the OFDMA scheme. The 3GPP and the 3GPP2 have started a standards project related to an enhanced cellular radio communication system using the OFDMA scheme.
FIG. 1 schematically illustrates a structure of a radio frame according to an LTE-A mobile communication system according to the related art.
Referring to FIG. 1, 1 radio frame includes 10 sub-frames, and each of 10 sub-frames includes 2 slots. So, indexes 0 to 9 are allocated to 10 sub-frames included in 1 radio frame, and indexes 0 to 19 are allocated to 20 slots included in 1 sub-frame.
FIG. 2 schematically illustrates a structure of a cellular radio communication system according to the related art.
In a cellular radio communication system in FIG. 2, a transmission/reception antenna is arranged at a center in each cell.
Referring to FIG. 2, in a cellular radio communication system including a plurality of cells, a particular User Equipment (UE) receives a radio communication service using a plurality of schemes as described above from a selected cell during a relatively long time, i.e., a semi-static time interval. For example, it will be assumed that the cellular radio communication system includes 3 cells, i.e., a cell 100, a cell 110 and a cell 120. The cell 100 provides a radio communication service to a UE 101 and a UE 102, the cell 110 provides a radio communication service to a UE 111, and the cell 120 provides a radio communication service to a UE 121. Base Stations (BSs) 130, 131 and 132 manage the cell 100, the cell 110 and the cell 120, respectively.
The UE 102 receiving the radio communication service using the cell 100 is located at a point relatively distant from the BS 130 compared with the UE 101. The UE 102 suffers from a relatively large interference from the BS 132 managing a service region of the cell 120, so the UE 102 receives data at a relatively slow data rate.
If the cells 100, 110 and 120 independently provide a radio communication service, a BS managing a service region of each of the cells 100, 110 and 120 transmits a Reference Signal (RS) so that a particular UE measures a downlink channel status of each of the cells 100, 110 and 120. If the cellular radio communication system is a 3GPP LTE-A mobile communication system, the RS is a Cell-Specific Reference Signal (CRS) or a Channel Status Information Reference Signal (CSI-RS).
Meanwhile, in a 3GPP LTE-A mobile communication system, a UE measures a channel status between a BS and the UE using a CRS or a CSI-RS transmitted in the BS, and feedbacks channel status information indicating the measured channel status to the BS. Information indicating that a reference signal which the UE uses for estimating a channel is the CRS or the CSI-RS is carried through transmission mode information which the BS transmits to the UE.
In the 3GPP LTE-A mobile communication system, a UE measures channel status between a BS and the UE using a CRS or a DeModulation Reference Signal (DM-RS) transmitted in the BS, and detects downlink data by performing a demodulation operation using the measured channel status. Information indicating that a reference signal which the UE uses for the demodulation operation is the CRS or the DM-RS is carried through transmission mode information which the BS transmits to the UE.
FIG. 3 schematically illustrates locations through which a CSI-RS is transmitted in a resource block in an LTE-A mobile communication system according to the related art. Each block in FIG. 3 indicates a Resource Element (RE) included in a resource block. Referring to FIG. 3, a vertical axis denotes a sub-carrier index, and a horizontal axis denotes Orthogonal Frequency Division Multiplexing (OFDM) symbol time.
Each of REs 200-219, CSI-RSs for distinguishing 2 CSI-RS antenna ports may be transmitted. That is, a particular BS broadcasts 2 CSI-RSs for a downlink measurement through a RE 200. As described in FIG. 2, in a cellular radio communication system including a plurality of cells, each cell allocates a RE included in a resource block, and a CSI-RS is transmitted through the allocated RE. For example, in FIG. 2, a CSI-RS may be transmitted through the RE 200 in the cell 100, a CSI-RS may be transmitted through a RE 205 in the cell 110, and a CSI-RS may be transmitted through a RE 210 in the cell 120. As described above, in a LTE-A mobile communication system of the related art, the reason why each cell transmits a CSI-RS using a different time resource and a different frequency resource is to prevent a mutual interference between CSI-RSs.
A sub-frame through which a CSI-RS is transmitted may be determined using an ICSI-RS as a parameter transmitted through a Radio Resource Control (RRC) message. Upon receiving the ICSI-RS, a UE determines TCSI-RS as a sub-frame period of a sub-frame through which a CSI-RS is transmitted and ΔCSI-RS as an offset of the sub-frame through which the CSI-RS is transmitted using Table 1.
TABLE 1CSI-RS periodicityCSI-RS subframe offsetCSI-RS-SubframeConfigTCSI-RSΔCSI-RSICSI-RS(subframes)(subframes)0-45ICSI-RS 5-1418ICSI-RS − 5 15-1420ICSI-RS − 1535-7440ICSI-RS − 35 75-15480ICSI-RS − 75
The UE receives a CSI-RS through a sub-frame satisfying a criteria expressed in Equation (1).(10nf+└ns/2┘−ΔCSI-RS)mod TCSI-RS=0  Equation (1)where, nf denotes a Radio Frame Number (RFN), and ns denotes a slot number included in a radio frame.
In FIG. 3, a DM-RS may be transmitted through REs 220 and 221. If one or two DM-RS transmission ports are used for a data transmission targeting a specific UE, a DM-RS is transmitted through the RE 220, and if more than two DM-RS transmission ports are used for the data transmission targeting the specific UE, the DM-RS is transmitted through the REs 220 and 221.
In FIG. 3, a CRS may be transmitted through a RE 231. The CRS is transmitted through a part of the RE 231 or all of the RE 231 according to the number of CRS transmission ports in the specific cell. A CRS transmission timing may be changed for each cell. That is, in FIG. 3, the CRS is transmitted at intervals of 3 sub-carriers starting from a sub-carrier with a sub-carrier index #0, however, a start position of a CRS transmission for each cell may be determined by applying a modulo operation to a Cell-ID for each cell. For example, the start position of the CRS transmission may be determined as a value of Cell-ID mod 6.
After assuming that downlink data, e.g., a Physical Downlink Shared CHannel (PDSCH) signal is not transmitted through a CSI-RS resource, a DM-RS resource, a CRS resource, and a control channel resource, the UE receives the PDSCH signal through a related resource among remaining resources.
The downlink data is not transmitted through a resource through which a SYNChronization (SYNC) signal is transmitted or a Physical Broadcast CHannel (PBCH) signal is transmitted as well as the resource through which the reference signal is transmitted. For example, the SYNC signal is transmitted through a part of OFDM symbols in sub-frames with sub-frame indexes #0, #5, and the PBCH signal is transmitted through a part of OFDM symbols in a sub-frame with a sub-frame index #0. The positions of the SYNC signal transmission and the PBCH signal transmission are determined according to an LTE-A mobile communication system standard, so the detailed description will be omitted.
In the LTE-A mobile communication system, each sub-frame may be set as a Multimedia Broadcast Multicast Service single Frequency Network (MBSFN) sub-frame, if a specific sub-frame is set as an MBSFN sub-frame, a CRS is not transmitted through resources except for a control channel resource in the specific sub-frame.
An MBSFN sub-frame configuration may be set for each cell, and each of the cells may have a different MBSFN sub-frame configuration. An MBSFN sub-frame may be used for a Physical Multicast CHannel (PMCH) transmission or a PDSCH transmission, if the MBSFN sub-frame is used for the PMCH transmission, an MBSFN reference signal is transmitted as a reference signal, and if the MBSFN sub-frame is used for the PDSCH transmission, a DM-RS and a CSI-RS are transmitted as reference signals.
In the LTE-A mobile communication system assuming that transmission/reception antennas are deployed at a center of each cell as shown in FIG. 2, a UE may detect a sub-frame number by detecting a SYNC signal, may detect MBSFN Sub-frame Configuration Information (SCI) and information on resources through which a CRS and a CSI-RS are transmitted by receiving a PBCH signal and cell associated-information, e.g., a System Information Block (SIB), and may detect position information for a DM-RS resource using PDSCH scheduling information transmitted through a control channel. So, each UE may receive downlink data by detecting a correct position of a resource through which a PDSCH signal is transmitted.
As described in FIG. 2, in an LTE-A mobile communication system assuming that a transmission/reception antenna is arranged at a center in each cell, a UE may detect an System Frame Number (SFN) by detecting a SYNC signal and detect sub-frames through which a CSI-RS is transmitted and sub-frames, through which a CSI-RS is not transmitted, which are collided with sub-frames through which a paging signal and system information are transmitted by receiving a PBCH signal and SIB messages.
In a cellular radio communication system in FIG. 2, there is a limitation for providing a high data rate to a UE located at a cell boundary due to interference from another cell. That is, a data rate for a high speed-data service is strongly influenced by a location of a UE. So, in a cellular radio communication system of the related art, it is possible that a relatively high data rate is provided to a UE located relatively close to a cell center, however, it is difficult for a high data rate to be provided to a UE located at a relatively far distance from a cell center.
In the LTE-A mobile communication system, a CoMP scheme in which a plurality of cells provide a communication service to a particular UE using a cooperation scheme has been proposed in order to provide a high data rate to a UE located at a cell boundary, and enlarge a service region providing the high data rate.
In the LTE-A mobile communication system, there is a need for a method of receiving a downlink data channel signal, e.g., a PDSCH signal by considering a reference signal resource, a SYNC signal resource, and a PBCH resource allocated in each of a plurality of cells in order to effectively use a CoMP scheme. The reference signal resource denotes a resource through which a reference signal is transmitted, the SYNC signal resource denotes a resource through which the SYNC signal is transmitted, and the PBCH resource denotes a resource through which the PBCH signal is transmitted.
In the LTE-A mobile communication system using the CoMP scheme, there is a need for distinguishing a sub-frame through which a PDSCH signal is transmitted among sub-frames transmitted from a plurality of cells and a sub-frame through which a PDSCH signal is not transmitted among the sub-frames in order that the UE effectively receives the PDSCH signal.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.